Patent document 1: JP-A-2010-283420
Patent document 1 discloses a wireless communication device performing wireless communication through an antenna. The wireless communication device includes inside a power detection device for detecting an output power of a signal outputted from the wireless communication device, and a power adjustment portion for adjusting the output power. A value of the output power, which has been detected by the power detection device, is outputted to the power adjustment portion. The power adjustment portion adjusts the output power based on the detection result, so that the output power of the signal outputted from the wireless communication device is adjusted to a desired output power value.
Since an antenna is placed separately from a wireless communication device when the wireless communication device mounted to a vehicle, an antenna module including the antenna may be connected with the wireless communication device by a coaxial cable. Hereinafter, the wireless communication device mounted to a vehicle (or used in a vehicle) is referred to as a vehicle communication apparatus.
The applicants of the present invention have found the following with respect to a vehicle communication apparatus.
Even when a vehicle communication apparatus differs individually, the vehicle communication apparatus needs to radiate a sending wave from an antenna with the same output power (corresponding to a reference power). However, when the antenna is placed physically apart from the wireless communication device through the coaxial cable, a sending power of the sending wave radiated from the antenna may be influenced by a loss in the coaxial cable. Since a length of the coaxial cable connecting the antenna and the wireless communication device differs for each vehicle model, an influence of the loss by the coaxial cable with respect to the sending power of the antenna may be differ for each vehicle model. Therefore, so as to eliminate differences of an output power between vehicle models, a set point of the output power of the wireless communication device may be adjusted for each vehicle model.
Even when the wireless communication device of patent document 1 is used as the wireless communication device of the vehicle communication apparatus, the power detection device is included to the wireless communication device, and a loss amount by the coaxial cable connecting the antenna module and the wireless communication device may be undetectable.
It may be considered that the power detection device includes the antenna module, so that the loss amount of the coaxial cable may be considered and the output power may be adjusted. However, a circuit configuration of an antenna module may become complicated and a manufacturing cost may increase with an arrangement of the power detection device.
Since the antenna module requires a packaging area for mounting an antenna and the power detection device, the antenna module may become large and a mountability of the antenna module may be lost.